1. Field of the Invention
The present invention relates, generally, to welding jigs; more especially to pipe flange welding jigs; and still more specifically to pipe flange welding jigs which have portable mobility and may be used to fabricate piping systems at remote field locations such as oil and gas exploration fields. The present invention also relates to methods for automatically presenting a pipe flange in a two-holed configuration.
2. Description of the Background Art
Welding jigs, and similar workpiece positioning tables and manipulators, are well known and have been devised in all manner of shapes and sizes. The common thread among devices heretofore proposed is the ability to restrain a workpiece in a desirable position and then manipulate that workpiece during a fabrication technique in a way which enhances production efficiency while maintaining accurate alignment of the components being assembled. A particularly commonplace environment for these types of devices is in the welding fabrication of, e.g., pipes and associated fittings; especially in the pre-fabrication of individual segments destined to comprise a fluid flow system.
In the context of pipe welding, the components invariably have a circular configuration where, typically, a pipe flange or similar terminal member must be secured to a length of pipe. It is crucial that the welding technique yields an effective joint which will be reliable in service. A welding jig or positioning table materially enchances the ability to achieve that aim; with two paramount aspects in mind.
First, most welders find their individual technique to be better laying a bead along a horizontal or substantially horizontal line when welding from above the work while, on the contrary, welding overhead poses greater difficulty. Intermediate difficulty is presented when laying a bead along a vertical; but that degree of difficulty is somewhat exacerbated when the vertical bead includes an arcuate component. Accordingly, welding jigs or similar work-positioning tables strive to present the workpiece in a manner allowing for its rotation during the welding procedure so that the welder may assume the most comfortable position vis-a-vis the work and manipulate the latter so that he or she is operating most efficiently.
The second conceptual aspect of importance in this arena is insuring the accurate lay-up of components during the welding procedure. Where one is called upon to fabricate a number of individual components, adding flanges, fittings, or the like to lengths of pipe, it is obviously crucial that the appropriate orientation from one component to another be maintained so that the finished, assembled product corresponds to the overall specifications of the piping system. This is a task easier said than done where pipes having elbows of various curvature, fittings of reduced or enlarged dimensions, valves and the like are fabricated individually but must ultimately piece together in a coherent, pre-established configuration. Positioning control during the welding process is the key to success or failure in this task.
It is now conventional to lay-up a pipe flange in a so-called "two-holed" configuration in order to maintain adequate and accurate alignment from one component to another ultimately to be assembled into a completed system. In capsule sum, a two-holed configuration simply refers to the alignment of the top two holes in the flange along a perfectly horizontal line. Then, when that flange is mated with an adjacent one for assembly, the flanges will align properly, and referencing all other components from this horizontal line will insure proper orientation thereof. Achieving this two-holed orientation reliably and accurately from component to component can be a very tedious endeavor.
All of the foregoing difficulties are compounded when the fabrication technique is to take place at a remote location, such as an oil or gas exploration field. In that environment the welder transports the shop to the field; carrying a portable welder, clamps, vises and other associated tools needed to assemble the piping system. The only available workplace is oftentimes the tail-gate of a truck; yet, under these less-than-desirable conditions, accuracy from piece to piece cannot be sacrificed.
Many have proposed welding jigs or similar positioners which are admirably suited for welding pipes, but most of which are limited to shop use and are ill-suited for field welding. Somewhat representative of one approach is the welding jig disclosed in U.S. Pat. No. 3,848,863. That apparatus is comprised of a pair of rails much like railroad tracks which support two movable carriages thereon. Pipe supports are located between the rails and are reciprocable between raised and lowered positions. Powered rollers associated with the support provide means to rotate a pipe during the welding process when joining it to a fitting such as a flange. Means are provided to adapt the device for welding fittings of various sizes and shapes in addition to flanges, including "T's", reducers, elbows and the like. Other apparatus of the same ilk, where plural stations are established by carriages or carriage-type members movable along tracks, are disclosed in U.S. Pat. Nos. 3,772,753 and 3,870,288. While these devices undoubtedly are highly suitable for their intended purposes, the same are conceptually ill-suited for use at remote locations where the importance of portable mobility is on a par with reliability and expediency. Simply put, these types of devices are too cumbersome, too complex, and are not adaptable for use, for example, in an exploration field where fabrication tends to be on an ad hoc as opposed to a production basis.
While there are other designs which admit of considerably simpler construction, such as those welding jigs disclosed in U.S. Pat. Nos. 2,909,137 and 3,239,209, none of the known prior devices can provide the combination of the necessary high degree of portable mobility with the desirability of precision lay-up. Further along these lines, no known apparatus can provide the advantages immediately aforesaid while also providing automatic indexing to present a pipe flange in the two-holed configuration repetitively and reliably; thereby eliminating a chronic source of rejects due to improper lay-up of components. Accordingly, the need exists for such a welding jig.